Moviegoers shelled out for Teenage Mutant Ninja Turtles, while Sylvester Stallone's action ensemble The Expendables 3 was easily outgunned in its weekend debut.

Paramount Pictures' rebooted reptiles took in US$28.4 million in the film's second weekend, according to yesterday's studio estimates. That far surpassed the limp US$16.2 million earned by Stallone's gang of aged - but buff - warriors.

The paltry, fourth-place total for The Expendables 3 is well below previous debuts in the Lionsgate franchise. The last two Expendables opened with US$34.8 million (August 2010) and US$28.6 million (August 2012). The third film is the first to be rated PG-13 in the previously R-rated series, which potentially signalled watered-down explosiveness to an audience that was largely over 25 years old anyway.

Expendables 3, which features a sprawling cast of Stallone, Arnold Schwarzenegger, Harrison Ford, Mel Gibson and others, also leaked online before its release, potentially damaging its impact in cinemas.

Instead, Marvel's The Guardians of the Galaxy came in second with US$24.7 million, bringing its three-week cumulative total to US$222 million for distributor Walt Disney. Along with the Nickelodeon Movies-produced Teenage Mutant Ninja Turtles, the cosmic romp starring Chris Pratt has helped restore some strength to the summer box office. Sequels are already in the works for both films.

After box office returns well off the pace of last summer, Hollywood has made a slight comeback in August, typically a dumping ground for studio leftovers. The summer overall is still running at a 15 per cent deficit from last year's record-breaking season, but the gap had once been above 20 per cent. August is up 14 per cent on last year.

"It's called the dog days of August for a reason," said Paul Dergarabedian, senior media analyst for box office tracker Rentrak. "But, thankfully, in a summer with a lot of ups and downs this has been a really good August."

A busy weekend slate also helped. Opening in third place was the 20th Century Fox buddy comedy Let's Be Cops, starring Jake Johnson and Damon Wayons Jr. It took in US$17.7 million.

Also debuting was the Lois Lowry adaptation The Giver, a dystopian young-adult tale starring Jeff Bridges and Meryl Streep. The Weinstein Co release opened with an estimated US$12.8 million.

These are estimated ticket sales for Friday through yesterday at US and Canadian theatres, according to Rentrak. Final domestic figures will be released today.